Cables including standardized connectors are used to connect audio devices. For example, a cable is equipped with a male connector at one end, whereas an audio device is equipped with a female connector.
One of the audio devices is a microphone. Microphones are composed of various microphone units. For example, a microphone unit of a condenser microphone has a high output impedance and thus requires an impedance converter. The impedance converter includes a field effect transistor (FET). In a tiepin or gooseneck condenser microphone, components, such as a microphone unit, of the microphone should be miniaturized and compactly disposed in a small case. The impedance converter is disposed inside the microphone unit for the same purpose.
The microphone further includes a circuit housing. The circuit housing is provided separately from the microphone unit and accommodates a low-cut circuit and an output circuit. The low-cut circuit and the output circuit accommodated in the circuit housing are collectively called a power module. The microphone is connected to an external device (e.g., a mixer or an amplifier) through a dedicated cable.
The microphone unit converts sound into electrical signals and transmits the electrical signals to the power module. The power module receives the electrical signals from the microphone unit and outputs the received electrical signals through the output circuit in the circuit housing.
The microphone is connected to the external device through a two-conductor shielded cable. The cable includes two conductors functioning as signal lines and shielding wires covering the conductors. It is noted that one of the signal lines in the cable may serve as a power line. In this case, the condenser microphone is energized though the conductor functioning as the power line. The signal line outputs the audio signals transmitted from the impedance converter via the power module to the external device. The shielding wires electrostatically shield and ground the power line and the signal line.
The cable including the signal line and the power line transmits unbalanced audio signals. The unbalanced signals are readily affected by external electromagnetic waves and thus are susceptible to external noise. For example, the external electromagnetic waves reach the cable and then enter the microphone unit or the power module through the cable. The external electromagnetic waves are detected by a semiconductor element included in the microphone unit or the power module. The audio signals are contaminated with electromagnetic waves in the form of noise. High-intensity electromagnetic waves can cause noise even in balanced signals. In other words, external electromagnetic waves can cause noise in signals output from the microphone regardless of the scheme of transmitting audio signals. In order to prevent the noise, the connectors that connect the microphone and the cable must be electromagnetically shielded.
For example, a connector mounted on the microphone (hereinafter referred to as “microphone connector”) enables a cable for the microphone (hereinafter referred to as “microphone cable”) to be plugged or unplugged into or from the microphone or the mixer. The microphone cable is equipped with a cable connector at an end. The cable connector is coupled to the microphone connector to electrically connect the cable to the microphone.
The cable connector includes, for example, three thin-tubular pin receivers (sockets). In this case, the three pin receivers of the cable connector can receive three pins included in the microphone connector.
The microphone connector includes a cylindrical metal receptacle and is mounted on the microphone or the mixer. The microphone connector has an electromagnetic-wave blocking structure. In the electromagnetic-wave blocking structure, a first pin for ground is electrically connected to the outer case of the microphone or the mixer and thus is grounded.
In a traditional electromagnetic-wave blocking structure, the connecting terminal of the first pin is wired to a grounded portion of the microphone or the mixer. Unfortunately, this structure introduces high-frequency current into the microphone or the mixer and thus leads to noise in output signals. In order to prevent the noise contamination, some connectors include receptacles each including a ceramic capacitor (chip component) soldered across the first pin and a second pin and a ceramic capacitor soldered across the first pin and a third pin. The ceramic capacitors across the respective pins cause short circuit of high-frequency current, thereby preventing the noise.
Unfortunately, ceramic capacitors directly soldered across the respective pins may be broken after repeated use. In specific, the pins of the microphone connector are slightly displaced by every plugging or unplugging of the microphone cable into or from the microphone connector. The slightly displaced pins apply stress to the ceramic capacitors via the solder and may break the ceramic capacitors.
In order to solve this problem, the present inventors have invented improved arrangement of ceramic capacitors for blocking external electromagnetic waves in a connector of an audio device, in particular, a microphone connector, as is disclosed in Japanese Unexamined Patent Application Publication No. 2006-067455 (hereinafter referred to as “PTL 1”).
According to PTL 1, pins of the microphone connector are connected to a circuit board such as a printed circuit board. The circuit board has specific wiring patterns and is mounted with capacitors connected to the wiring patterns. In specific, the capacitors on the circuit board are each connected across the wiring pattern coupled to a ground pin and a wiring pattern coupled to other pin. These capacitors cause short circuit of high-frequency current, thereby blocking external electromagnetic waves.
In the connector disclosed in PTL 1, the stress by the plugging or unplugging of a cable is not applied to the capacitors for blocking electromagnetic waves. This configuration can protect the capacitors, for example, ceramic capacitors, against damaging by physical force.